The present invention relates generally to a layout design for integrated circuit (IC), and, more particularly, to a method for power line layout in modular ICs.
IC layout is the representation of an integrated circuit in terms of planar geometric shapes that correspond to shapes actually drawn on photo-masks used in semiconductor device fabrication.
Power supply voltages are typically supplied to an IC chip from an external power supply source. The power supply voltages connect to the IC chip through bond pads on the IC chip. The power supply voltages are routed from the bond pads to transistors in the IC chip through metal lines and vias formed in one or more metal layers.
Since the metal lines have resistance, transistors at an end of a long metal line will have a lower power supply voltage than transistors at the beginning of the long metal lines. The speed of transistors depends in part on the magnitude of the power supply voltages they receive. Differences in power supply voltages can cause timing problems such as clock skew or increased propagation delay of gates and flip-flops. So proper power line layout is very important to the performance of the IC chips, especially when the chip size is relatively big.
One kind of power line routing is to run a ring-type power line along a peripheral of each section of the chip.
Traditional power ring structures at the edges of an IC chip form the backbone of the power distribution system. The metal lines extend from the ring structures to the center of the IC chip. The metal lines are then coupled to transistors. One drawback of this kind of power routing scheme is the voltage drop at the center of the IC chip due to the resistance of metal lines. Another draw back is that running a power ring may increase area overhead.
Power mesh is another traditional way of power routing, in which multiple parallel power lines are routed from one side of the IC chip to the other. A disadvantage with this kind of power routing scheme is that the power lines are routable only in one direction. Signal lines in the same metal layer as the power lines are also routable in only one direction.
As such, what is desired is an efficient power line routing scheme that allows both the power lines and the signal lines routable in both horizontal and vertical directions.